This invention relates to a pressure sensor of the type that is used in a blood pressure transducer.
The blood pressure transducer of the type disclosed in copending application Ser. No. 009,643, filed Jan. 27, 1987, pending employs a silicon sensor. The silicon sensor is very small, being a fraction of a square inch in area. It is circular in cross section and has a Wheatstone bridge strain gauge formed of piezo-resistive elements diffused into the silicon substrate. The silicon substrate is chemically etched away on the surface opposite the Wheatstone bridge so as to form a thin silicon diaphragm that flexes when subjected to pressure causing the resistors in the Wheatstone bridge strain gauge to be stressed to produce an indication of the applied pressure. The manufacturing process for the silicon sensor is necessarily expensive. Further, the sensor is temperature-sensitive and therefore requires a temperature compensation circuit.
Strain gauges have been formed in other ways. It is known to form a strain gauge by depositing a thick film resistor on alumina. The resistor must be baked at a high temperature of the order of 800.degree. F. Hence, a ceramic such as alumina is required as the substrate.
It is also known to form strain gauges from conductive polymers, again using alumina as a substrate. These thick film resistor and conductive polymer strain gauges have all been massive compared to the tiny silicon sensor.